In his Tucson speech, Presi dent Obama rightly said that “terrible things happen for reasons that defy human understanding.” Why that morning? Why Gabby Giffords? These and other questions can’t be answered, but at a more pedestrian level, the massacre isn’t so mysterious: Someone displaying all the symptoms of untreated schizophrenia killed people.

This is not an extraordinarily rare or inexplicable occurrence. According to the psychiatrist E. Fuller Torrey, 4 million people in the United States have serious mental illnesses, and 1.8 million of them go untreated. Two hundred thousand are homeless, and 300,000 are in jail or prison. Tormented by depression or delusions, about 15 percent kill themselves, and they commit about 1,600 murders a year.

Obama was too sweeping when he said we shouldn’t point fingers. Our ire should be directed at the mental-health “advocates,” federal bureaucrats and crusading civil libertarians who fight to maintain a status quo that makes it so hard to treat the mentally ill. They are the madness lobby.

They aren’t responsible for Jared Loughner or his crimes. They do deserve the blame for a system that willfully lets people fall through the cracks and pretends diseased minds can make rational decisions. At its best, this system is cruel in abandoning the ill to their suffering; in exceptional cases, it is reckless in leaving dangerous people to do harm to themselves or others. The madness lobby helps make the lunatic act of violence a routine part of the American landscape.

A group of “anti-psychiatrist” thinkers provided the philosophical impetus for emptying our mental institutions. Thomas Szasz, Michel Foucault and others ably demonstrated the power of idiot ravings to increase the sum total of human misery. Szasz compared psychiatry to slavery, while idealistic lawyers who wanted to vindicate the civil rights of patients launched an assault on commitment laws.

In a combination of foolish budget-cutting and misconceived compassion (some institutions were indeed horrors), states began to dump people out of mental hospitals in the 1960s. In his book “The Insanity Offense,” Torrey documents how as the numbers of mentally ill in institutions declined throughout the ’70s and ’80s, the numbers on the streets or in jails rose. For many mentally ill, deinstitutionalization was essentially a shuffle — from hospital to prison.

In the 1970s, a Wisconsin court struck down the state’s civil-commitment law in a decision that reverberated nationally. In writing his 2008 book, Torrey visited Alberta Lessard, the schizophrenic woman whose case prompted the decision. Still untreated, she had spent time homeless and had never held a job, had been charged with 10 crimes and lived with constant delusions of people persecuting her.

In the wake of Lessard and similar decisions, it became the rule in most states to wait until someone is on the cusp of suicide or murder to commit them. It nearly became impossible to force the mentally ill to take their medication, in or out of the hospital.

Today, even with the human wreckage of its handiwork all around us, the madness lobby persists. The federal Substance Abuse and Mental Health Services Administration funds efforts to liberate the seriously ill from their treatment. Writing in The Weekly Standard, Sally Satel recounted a case in Maine where a SAMHSA-funded outfit got a patient out of the hospital over the objections of his parents; he killed his mother with a hatchet two months later.

Mental illness is the only disease that has an influential lobby devoted to not treating it.

Arizona has a quite sensible legal regime. It allows the imposition of care on someone who is “persistently and acutely disabled” and “likely to benefit from treatment.” But apparently no one brought Jared Loughner to the attention of the mental-health system.

Perhaps we won’t seize on this particular senseless murder by someone who is deeply disturbed to reconsider our neglect of the mentally ill. But don’t worry: It will happen again.